It is well known to construct a well by rotating a drill bit mounted to the lower end of string of drill pipe to drill a borehole into subsurface soil formations, and then to install a tubular casing (or liner) string in the borehole to prevent adjacent soil materials from falling into the borehole. After the borehole has been cased, a string of production tubing is run into the well to carry well fluids to the surface.
In cases where a top-drive-equipped drilling rig is used for the drilling operation (as opposed to a “rotary table”), it is increasingly common to install (or “run”) the casing using so-called casing running tools (CRTs) operatively engaged by the top drive. In an alternative method of constructing a well commonly called “drilling with casing”, the drill bit is mounted to the end of a casing string such that the casing string acts as the drill string and remains in the borehole after completion of drilling operations, thus eliminating the need to remove the drill string to install casing. In either of these methods, the top drive must transmit torque and axial loads to the tubular string (i.e., drill string or casing string), and a sealed conduit for drilling and completion fluids must be provided between the top drive and the tubular string.
Among the routine procedures carried out during well drilling and completion operations are the assembly (or “make-up”) of the tubular string by means of threaded connections between adjacent lengths (or “joints”) of pipe, and the disassembly (or “break-out”) of these connections. The upper end of each joint of pipe in the tubular string typically carries a female thread (and is referred to as a “box end”), and the lower end of each joint carries a complementary male thread (and is referred to as a “pin end”). To add a new joint to the tubular string, the upper end of the string is suspended by gripping apparatus commonly known as “slips” mounted in the rig floor, and the pin end of the new joint is “stabbed” into the box end at the top of the string suspended in the slips. The new joint is then rotated to make up a threaded connection with the suspended string.
Such threaded connections usually need to be made up to a controlled torque to form a mechanical, metal-to-metal seal between the ends of the pipe joints, and to ensure that drilling loads (or casing running loads) can be properly transmitted through the connection. In more traditional drilling operations using a rotary table, tubing joints are typically made up using power tongs to both apply and control the rotation and torque. However, in drilling operations using top-drive-equipped rigs, the top drive may be used not only to assemble drill strings, but also for make-up (and break-out) of tubing string connections.
For threaded connections for casing strings and production strings, the applied make-up torque typically needs to be within a relatively more tightly-controlled range than for drill strings, to ensure proper function of the connection. These connections may incorporate torque shoulders and metal-to-metal seals requiring precise make-up control (commonly referred to as “torque-turns” control), and they tend to be more sensitive to over-torque damage than drill pipe connections. These connections are relied upon to provide a high level of leakage integrity. If the make-up torque of a connection is too low, the torque shoulders and metal-to-metal seals might not be properly engaged, resulting in poor connection performance. If the make-up torque is too high, the connection may be damaged, thereby compromising its seal performance and/or structural capacity.
Generally speaking, the torque-turns (i.e., rotational position) control systems of top drives only anticipate the control needs for make-up of tool joint connections used on drill pipe, and not the needs for relatively much more rapid response and more precise torque-turns control for casing and production tubing connection make-up. Furthermore, the large size of many top drive units makes such rapid and precise control difficult in any case. Accordingly, there is an increased need for means for better managing the torque loads applied during make-up operations using top drives, particularly in the context of casing and production tubing strings.